feat: enable token-level streaming and fix duplicate message bubble

Backend:
- Add includePartialMessages: true to SDK query options
- Handle stream_event/content_block_delta for real-time text streaming
- Skip text/thinking blocks from complete assistant messages (already
  streamed via deltas) to avoid duplication
- Change default result summary to empty string

Flutter:
- Only show CompletedEvent summary when no assistant text was streamed
  (prevents duplicate message bubble)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

it0_app/lib/features/chat/presentation/providers/chat_providers.dart

@@ -230,7 +230,12 @@ class ChatNotifier extends StateNotifier<ChatState> {
         );
 
       case CompletedEvent(:final summary):
-        if (summary.isNotEmpty) {
+        // Only show summary as a message if there were no assistant text messages
+        // (avoids duplicate bubble when the SDK already streamed the full response)
+        final hasAssistantText = state.messages.any(
+          (m) => m.role == MessageRole.assistant && m.type == MessageType.text && m.content.isNotEmpty,
+        );
+        if (summary.isNotEmpty && !hasAssistantText) {
           _appendOrUpdateAssistantMessage(summary, MessageType.text);
         }
         state = state.copyWith(agentStatus: AgentStatus.idle);

packages/services/agent-service/src/infrastructure/engines/claude-agent-sdk/claude-agent-sdk-engine.ts

@@ -107,6 +107,7 @@ export class ClaudeAgentSdkEngine implements AgentEnginePort {
           maxBudgetUsd: params.maxBudgetUsd,
           env,
           abortController,
+          includePartialMessages: true,
           allowDangerouslySkipPermissions: true,
           permissionMode: 'bypassPermissions',
           stderr: (data: string) => {
@@ -273,6 +274,7 @@ export class ClaudeAgentSdkEngine implements AgentEnginePort {
         prompt: message,
         options: {
           resume: sdkSessionId,
+          includePartialMessages: true,
           env,
           abortController,
           allowDangerouslySkipPermissions: true,
@@ -352,15 +354,28 @@ export class ClaudeAgentSdkEngine implements AgentEnginePort {
   private mapSdkMessage(message: any): EngineStreamEvent[] {
     const events: EngineStreamEvent[] = [];
 
-    if (message.type === 'assistant') {
+    if (message.type === 'stream_event') {
+      // Token-level streaming from includePartialMessages: true
+      const streamEvent = message.event;
+      if (!streamEvent) return events;
+
+      if (streamEvent.type === 'content_block_delta') {
+        const delta = streamEvent.delta;
+        if (delta?.type === 'text_delta' && delta.text) {
+          events.push({ type: 'text', content: delta.text });
+        } else if (delta?.type === 'thinking_delta' && delta.thinking) {
+          events.push({ type: 'thinking', content: delta.thinking });
+        }
+      }
+      // Ignore content_block_start/stop/message_start/message_stop — they are structural
+    } else if (message.type === 'assistant') {
+      // Complete assistant message (also emitted after streaming)
+      // When streaming is enabled, skip full blocks to avoid duplicate text
+      // Only forward tool_use and tool_result which aren't streamed as deltas
       const content = message.message?.content;
       if (Array.isArray(content)) {
         for (const block of content) {
-          if (block.type === 'thinking') {
-            events.push({ type: 'thinking', content: block.thinking ?? '' });
-          } else if (block.type === 'text') {
-            events.push({ type: 'text', content: block.text ?? '' });
-          } else if (block.type === 'tool_use') {
+          if (block.type === 'tool_use') {
             events.push({
               type: 'tool_use',
               toolName: block.name ?? 'unknown',
@@ -376,12 +391,13 @@ export class ClaudeAgentSdkEngine implements AgentEnginePort {
               isError: block.is_error ?? false,
             });
           }
+          // text and thinking blocks are already streamed via stream_event deltas
         }
       }
     } else if (message.type === 'result') {
       events.push({
         type: 'completed',
-        summary: message.result ?? 'Task completed',
+        summary: message.result ?? '',
         tokensUsed: message.usage
           ? (message.usage.input_tokens ?? 0) + (message.usage.output_tokens ?? 0)
           : undefined,